1. Technical Field
The present disclosure relates to a printer that conveys the recording medium toward a platen using a paper feed mechanism including a paper feed roller and a pressure roller.
2. Related Art
The paper feed roller can be deflected by the pressure from the pressure roller in a printer that has a paper feed roller and a pressure roller on the upstream side of the platen in the paper feed direction. For example, when the conveyance path is wide and the pressure of the pressure roller is increased to increase the media conveyance force, deflection of the paper feed roller increases. In this event, the middle of the width of the recording medium that is pressed by the paper feed roller also bends and sags greatly. When the recording medium is fed to the platen while thus sagging, the middle of the width of the recording medium may catch on the platen and a paper jam may occur in front of (on the upstream side of) the platen.
A paper feed mechanism that conveys the recording medium while the paper feed roller is in a deflected state is disclosed in JP-A-2009-202978. The image reading device (scanner) taught in JP-A-2009-202978 causes the drive roller (paper feed roller) to bend to the downstream side in the conveyance direction. The left and right ends of the drive roller therefore slope from the ends in toward the center, and the paper can be conveyed without being wrinkled. Because the relative positions of the drive roller and driven roller (pressure roller) are thus offset in the paper conveyance direction at the center of the drive roller, the paper nipping position in the center of the drive roller moves down from the nipping position at the left and right ends of the drive roller. In JP-A-2009-202978, the driven roller is moved downstream in the conveyance direction according to the amount of deflection across the drive roller. As a result, the difference in the height of the nipping positions at the left and right ends of the drive roller and the nipping position in the middle of the drive roller is corrected, and downward deflection of the middle of the width of the paper is prevented. The leading end of the paper can therefore be prevented from catching on the image scanning unit.
The device taught in JP-A-2009-202978 eliminates variation in the nipping position resulting from the drive roller (paper feed roller) bending to the downstream side in the media conveyance direction, and thereby eliminates sagging in the paper, but does not align the height of the nipping positions when parts of the drive roller move up or down, and does not correct sagging in the paper caused by pressure from the driven roller causing the drive roller to bend to the downstream side. Furthermore, the height of the nipping position will change with deformation of the driven roller by simply moving the driven roller in the conveyance direction because the driven roller located in the middle of the drive roller is made from a flexible material, but if the driven roller is a roller that does not change shape, aligning the height of the nipping positions with this simple operation is difficult.